Ionic Compounds What holds them together?

Ion Pair Energy Attractions:

Ion Pair Energy The big picture:

Ion Pair Energy: Trends for charges and ion size

Ion-Pair Energy Energy released when gas phase ions combine to form the pair of ions. U = lattice energy N = Avogadro’s Number z = charges e = charge on electron = 1.602 x 10-19 C o = 8.854 x 10-12 C2/mJ ro = sum of radii n = average Born exponent NaCl: ro = 283 pm = 2.83 x 10-10 m; A = 1.748

Madelung Constant:

Madelung Constant:

Madelung Constant:

Madelung Constant: Concentric cube approach

Lattice Energy Energy released when gas phase ions combine to form the ionic solid. U = lattice energy N = Avogadro’s Number A = Madelung constant z = charges e = charge on electron = 1.602 x 10-19 C o = 8.854 x 10-12 C2/mJ ro = sum of radii n = average Born exponent NaCl: ro = 283 pm = 2.83 x 10-10 m; A = 1.748

Properties

Lattice Holes and Structure Selection

ZnS

Measuring Lattice Energies: Born-Haber Cycles Hf (NaCl) = -411 kJ/mol Hatomization(Na) = 108 kJ/mol Cl-Cl bond energy = 242 kJ/mol IE(Na) = 502 kJ/mol EA(Cl) = -349 kJ/mol

Question: Is the driving force for formation of NaCl the electron transfer from Na to Cl? That is, is it because Cl wants Na’s valence electron more than Na wants it?

Why does MgF2 form instead of MgF or MgF3?